HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Blonquist, J. M. Articles by Robinson, D. A. Search for Related Content PubMed Articles by Blonquist, J. M., Jr. Articles by Robinson, D. A. GeoRef GeoRef Citation Agricola Articles by Blonquist, J. M. Articles by Robinson, D. A. Related Collections Water Management Soil Methods/Instrumentation Time Domain Reflectometry, TDR

SPECIAL SECTION: SOIL WATER SENSING

Standardizing Characterization of Electromagnetic Water Content Sensors

Part 2. Evaluation of Seven Sensing Systems

Dep. of Plants, Soils and Biometeorology, Utah State University, 4820 Old Main Hill, Logan, UT, USA 84322-4820
^* Corresponding author (jmarkb{at}cc.usu.edu)

Received 28 September 2004.

Transmission line-type electromagnetic (EM) methods for estimating soil volumetric water content (_v) have advanced significantly in recent years, with many sensing systems now available. To estimate _v, EM systems make use of the dependence of soil dielectric permittivity on _v. However, a standard method for characterizing and comparing EM system measurement capability has not been established. Our objective was to evaluate the permittivity measurement ability of seven different EM sensing systems using readily available media. Sensing system outputs were converted to real permittivity (') values and compared with reference ' values in lossless and lossy dielectric liquids under four different test conditions: nonrelaxing and nonconducting (NR-NC), relaxing and nonconducting (R-NC), nonrelaxing and electrically conducting (NR-C), and temperature variation in NR-NC. The higher frequency broadband sensing systems, consisting of two time domain reflectometry (TDR) systems and one time domain transmissometry (TDT) system, deviated from a network analyzer by less than ±2.94 ' units across a ' range of 12.7 to 78.5 in NR-NC media. Two lower frequency impedance sensing systems deviated from the network analyzer by less than ±3.94 ' units across a ' range of 12.7 to 36.5 in the same media. Measurement of ' using higher frequency broadband sensing systems was impacted more by bulk electrical conductivity (_b) and temperature (T) than by dielectric relaxation. Imaginary permittivity values (due only to relaxation, ^''_rel) of up to 14.5 in R-NC media resulted in ' errors of ±0.511, whereas _b values ranging from 0 to 2 dS m^–1 in NR-C media resulted in ' errors of ±2.69 and T values ranging from 5 to 40°C resulted in ' errors of ±4.89. Determination of ' using lower frequency sensing systems—including one transmission line oscillator, two impedance probes, and one capacitance probe—was impacted more by _b than by T and ^''_rel. For the lower frequency sensors (and the same ranges of _b, T, and _rel), _b resulted in ' errors of ±111, T resulted in ' errors of ±6.59, and ^''_rel resulted in ' errors of ±3.28. The effects of ^''_rel, _b, and T on permittivity measurement accuracy is to a large extent dependent on measurement frequency, with higher frequency broadband sensing systems generally yielding better measurements.

Abbreviations: EM, electromagnetic • NR-C, nonrelaxing and electrically conducting • NR-NC, nonrelaxing and nonconducting • R-C, relaxing and conducting • R-NC, relaxing and nonconducting • TDT, time domain transmissometry • TDR, time domain reflectometry

This article has been cited by other articles:

				D. A. Robinson, C. S. Campbell, J. W. Hopmans, B. K. Hornbuckle, S. B. Jones, R. Knight, F. Ogden, J. Selker, and O. Wendroth Soil Moisture Measurement for Ecological and Hydrological Watershed-Scale Observatories: A Review Vadose Zone J., February 25, 2008; 7(1): 358 - 389. [Abstract] [Full Text] [PDF]

				M. S. Seyfried and L. E. Grant Temperature Effects on Soil Dielectric Properties Measured at 50 MHz Vadose Zone J., October 8, 2007; 6(4): 759 - 765. [Abstract] [Full Text] [PDF]

				R. B. Thompson, M. Gallardo, M. D. Fernandez, L. C. Valdez, and C. Martinez-Gaitan Salinity Effects on Soil Moisture Measurement Made with a Capacitance Sensor Soil Sci. Soc. Am. J., September 28, 2007; 71(6): 1647 - 1657. [Abstract] [Full Text] [PDF]

				S. R. Evett and G. W. Parkin Advances in Soil Water Content Sensing: The Continuing Maturation of Technology and Theory Vadose Zone J., November 11, 2005; 4(4): 986 - 991. [Abstract] [Full Text] [PDF]

				D. A. Robinson, T. J. Kelleners, J. D. Cooper, C. M. K. Gardner, P. Wilson, I. Lebron, and S. Logsdon Evaluation of a Capacitance Probe Frequency Response Model Accounting for Bulk Electrical Conductivity: Comparison with TDR and Network Analyzer Measurements Vadose Zone J., November 11, 2005; 4(4): 992 - 1003. [Abstract] [Full Text] [PDF]

				S. B. Jones, J. M. Blonquist Jr., D. A. Robinson, V. P. Rasmussen, and D. Or Standardizing Characterization of Electromagnetic Water Content Sensors: Part 1. Methodology Vadose Zone J., November 11, 2005; 4(4): 1048 - 1058. [Abstract] [Full Text] [PDF]